Fracture propagation law of temporary plugging and diversion fracturing in shale reservoirs under completion experiments of horizontal well with multi-cluster sand jetting perforation

This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.

Optimization of the Plugging Agent Dosage for High Temperature Salt Profile Control in Heavy Oil Reservoirs

After steam discharge in heavy oil reservoirs,the distribution of temperature,pressure,and permeability in different wells becomes irregular.Flow channels can easily be produced,which affect the sweep efficiency of the oil displacement.Previous studies have shown that the salting-out plugging method can effectively block these channels in high-temperature reservoirs,improve the suction profile,and increase oil production.In the present study,the optimal dosage of the plugging agent is determined taking into account connection transmissibility and inter-well volumes.Together with the connectivity model,a water flooding simulation model is introduced.Moreover,a non-gradient stochastic disturbance algorithm is used to obtain the optimal plugging agent dosage,which provides the basis for the high-temperature salting-out plugging agent adjustment in the field.

Thermo-sensitive polymer nanospheres as a smart plugging agent for shale gas drilling operations

Emulsifier-free poly（methyl methacrylate-styrene） [P（MMA-St）] nanospheres with an average particle size of 100 nm were synthesized in an isopropyl alcoholwater medium by a solvothermal method. Then, through radical graft copolymerization of thermo-sensitive mono- mer N-isopropylacrylamide （NIPAm） and hydrophilic monomer acrylic acid （AA） onto the surface of P（MMA- St） nanospheres at 80 ℃, a series of thermo-sensitive polymer nanospheres, named SD-SEAL with different lower critical solution temperatures （LCST）, were prepared by adjusting the mole ratio of NIPAm to AA. The products were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, particle size distribution, and specific surface area analysis. The temperature-sensitive behavior was studied by light transmittance tests, while the sealing performance was investigated by pressure transmission tests with Lungmachi Formation shales. The experimental results showed that the synthesized nanoparticles are sensitive to temperature and had apparent LCST values which increased with an increase in hydrophilic monomer AA. When the temperature was higher than its LCST value, SD- SEAL played a dual role of physical plugging and chemical inhibition, slowed down pressure transmission, and reduced shale permeability remarkably. The plugged layer of shale was changed to being hydrophobic, which greatly improved the shale stability

Development of degradable pre-formed particle gel(DPPG)as temporary plugging agent for petroleum drilling and production

Temporary plugging agent(TPA)is widely used in many fields of petroleum reservoir drilling and production,such as temporary plugging while drilling and petroleum well stimulation by diverting in acidizing or fracturing operations.The commonly used TPA mainly includes hard particles,fibers,gels,and composite systems.However,current particles have many limitations in applications,such as insufficient plugging strength and slow degradation rate.In this paper,a degradable pre-formed particle gel(DPPG)was developed.Experimental results show that the DPPG has an excellent static swelling effect and self-degradation performance.With a decrease in the concentration of total monomers or cross-linker,the swelling volume of the synthesized DPPG gradually increases.However,the entire self-degradation time gradually decreases.The increase in 2-acrylamide-2-methylpropanesulfonic acid(AMPS)in the DPPG composition can significantly increase its swelling ratio and shorten the self-degradation time.Moreover,DPPG has excellent high-temperature resistance(150°C)and high-salinity resistance(200,000 mg/L NaCl).Core displacement results show that the DPPG has a perfect plugging effect in the porous media(the plugging pressure gradient was as high as 21.12 MPa),and the damage to the formation after degradation is incredibly minor.Therefore,the DPPG can be used as an up-and-coming TPA in oil fields.

LEAKAGE-PLUGGING WHILE DRILLING AND PLUGGING AGENTS

This paper describes a series of plugging agents which have been developed these years by the authors. The features of these agents can bestated as: (1) Stopping losses without stopping drilling; (2) High ratio of success; (3) Improving fluids properties; (4) Suiting to many types of losses, even large cracks and caves; (5) Perfect efficiency in different conditions of pollution such as calcium, salt pollution and high temperature; (6) Sufficient resources of raw materials, nopoison, noharm, no pollution to the environment; (7) Convenience in use; (8) Lower cost. The properties, mechanisms and applications of these agents are also described in this paper.

A bull-heading water control technique of thermo-sensitive temporary plugging agent

Aimed at the disadvantages of secondary damage to oil layers caused by the conventional bull-heading water control technique, a thermo-sensitive temporary plugging agent for water control was synthesized by water solution polymerization and applied in the field with a new secondary temporary plugging technique. The optimization and performance evaluation of thermo-sensitive temporary plugging agent were carried out through laboratory experiments. The optimized formula is as follows:(6%-8%) acrylamide +(0.08%-0.12%) ammonium persulfate +(1.5%-2.0%) sepiolite +(0.5%-0.8%) polyethylene glycol diacrylate. The thermo-sensitive temporary plugging agent is suitable for formation temperatures of 70-90 ?C, it has high temporary plugging strength(5-40 k Pa), controllable degradation time(1-15 d), the apparent viscosity after degradation of less than 100 m Pa?S and the permeability recovery value of simulated cores of more than 95%. Based on the research results, secondary temporary plugging technique was used in a horizontal well in the Jidong Oilfield. After treatment, the well saw a drop of water cut to 27%, and now it has a water cut of 67%, its daily increased oil production was 4.8 t, and the cumulative oil increment was 750 t, demonstrating that the technique worked well in controlling water production and increasing oil production.

Research and Advances of Silicate Plugging Agent in the Oilfields

The paper overviews the research and application of silicate plugging agent, according to the different mechanisms and application forms, the plugging agent is divided into silicate gel, silicate precipitation, silicate/polymer, silicate/surfactant, silicate gel/foam and so on. This paper chiefly introduces the conception, mechanism and development tendency of the different systems mentioned above. The development tendency manifests as fully utilize personal properties and cooperate with other plugging agents or technologies, including the study of reaction mechanism, combination of plugging agent, grasping water flood timing, developing deep profile control and water shutoff technology, combining with other measures (chemicals huff and puff), in order to play the role of such blocking agents, further enhance oil recovery.

Microstructure Formation and Degradation Mechanism of Cementitious Plugging Agent Slurries

The hydration products and microstructure of class G oil well cement and a newly developed plugging agent （YLD） slurries cured in the simulated temperature and pressure environment, which was of similar temperature and pressure with those at the bottom of oil well in a normal depth, were investigated using XRD, TG and SEM. Severe leakage is confirmed at the interface between hardened slurries and steel tube during the dynamically curing process, which induces the quick loss of cementing property of slurries. This should be the dominating cause of degradation of class G oil well cement slurry. A secondary hydration process can take place at the eroded interface of hardened YLD plugging agent slurry. Newly formed C-S-H gel has a self-healing effect to repair the damaged interface, which unceasingly maintains the cementing property of the YLD plugging agent slurry. Therefore, the effective using period of YLD plugging agent can be prolonged.

Degradable preformed particle gel as temporary plugging agent for low-temperature unconventional petroleum reservoirs:Effect of molecular weight of the cross-linking agent

The development of unconventional petroleum resources has gradually become an important succession for increasing oil production.However,the related engineers and researchers are paying more and more attention to the application of temporary plugging agents(TPAs)for their efficient development.TPAs can expand the stimulated reservoir volume(SRV)and facilitate the flow of oil and gas to the bottom of the well.Particle-gels used as temporary plugging agents have the characteristics of the simple injection process,good deformation,high plugging strength,and complete self-degradation performance,which have been widely applied in recent years.In this paper,five samples of DPPG polymerized by different molecular weights of cross-linking agents were prepared.In addition,infrared spectroscopy analysis,differential calorimetry scanning(DSC)analysis,static particle gel swelling and degradation performance evaluation experiments,and dynamic temporary plugging performance experiments in cores were conducted at 34°C.Results show that as the molecular weight of the cross-linking agent(at 0.01 g)in the DPPG molecule decreased from 1,000 to 200 Da,the fewer cross-linking sites of DPPG,the looser the microscopic three-dimensional mesh structure formed.The swelling ratio increased from 7 to 33 times.However,the complete degradation time increased from 40 to 210 min.Moreover,the DSC results confirmed that the higher the molecular weight of the cross-linking agent,the worse is chemical stability and the more prone it to self-degradation.DPPG samples had good temporary plugging performance in reservoir cores.DPPGs prepared by the cross-linking agent with smaller molecular weight has a stronger swelling ratio,higher gel strength,and greater plugging strength in the core permeabilities.Moreover,the degraded DPPG is less damaging to the cores.However,their slower degradation rates take a slightly longer times to reach complete degradation.The results of this paper can provide new ideas and a theoretical basis for the development of particle gel-type temporary plugging agents(TPA)with controllable degradation time in low-temperature reservoirs.It can help to expand the application range of existing DPPG reservoir conditions.

Synthesis and Evaluation of a Water-Swelling Polymer Plugging Agent SWL-1

In this paper, to solve the problems of low water absorption and weak pressure bearing capacity of current plugging materials, acrylic acid (AA), acrylamide (AM), and sodium allyl sulfonate (SAS) are used as monomers, and soluble starch is used as grafting. Material, the use of free radical aqueous solution method to synthesize the plugging agent SWL-1 with good water absorption and strong salt resistance. The monomer ratio is set as n (AA):n (AM):n (SAS) = 5:2:1, the experimental synthesis temperature is 70°C, and the orthogonal experiment is used to determine the experimental synthesis conditions as AA neutralization degree 80%, The amount of initiator is 0.60%, the amount of crosslinking agent is 0.50%, the ratio of monomer to starch is 7:1, and the amount of calcium carbonate is 13%. The comprehensive evaluation of the performance of the plugging agent SWL-1 shows that the water absorption performance at 60°C is the best 268.78 g/g, and the water absorption performance in 8% NaCl, 0.9% CaCl2 and composite brine is 21.5 g/g, 12.5 g/g and 24.9 g/g, indicating good resistance to sodium and calcium, the water retention rate is still higher than 30% after 15 days at 160°C. The sand bed plugging test found that the maximum pressure of SWL-1 was 7 MPa, and the crack plugging test found that when the crack width was 1 mm, 2 mm, and 3 mm, the maximum compressive strength of SWL-1 was 10 MPa. The acid solubility test showed that the maximum pressure was 10 MPa. The highest rate is 86.38%.

The Research of Polymer Film-Forming Plugging Agent for Drilling Fluid

In order to improve the plugging and anti-collapse performance of water-based drilling fluid,a polymer film-forming plugging agent LWFD is synthesized by emulsion polymerization.The effect of the agent on rheology,API filtration loss,lubricity and film plugging of polymer drilling fluid and cationic drilling fluid is evaluated in laboratory.The experimental results show that the agent has little effect on the rheology and filtration loss of polymer drilling fluid and cationic drilling fluid,and can improve the lubricity of drilling fluid.The synthesized polymer film-forming plugging agent LWFD has good plugging properties for sand discs with different permeabilities,and the agent can effectively improve the film-forming plugging and temperature resistance of drilling fluid when combined with the inorganic nano-plugging agent NMFD.The high performance polymer drilling fluid formed by introducing polymer film-forming plugging agent LWFD and inorganic nano-plugging agent NMFD into polymer drilling fluid has comparable performance as Halliburton’s SHALEDRIL high performance drilling fluid,which can meet the requirements of on-site drilling and has application value.

Study on Plugging Technology in Oil Test

In view of the shortcomings of poor temperature resistance, poor pumpability and poor pressure-bearing capacity of commonly used gel plugging materials, polyacrylamide (HPAM) and N,N-methylene bisacrylamide (BIS) were selected for crosslinking and compounding to make a new type of gel plugging material with high temperature and pressure resistance. The compressive strength and yield stress were measured by inverted observation method to evaluate the gel strength. The anti-temperature, anti-pressure, anti-dilution and gel-breaking properties of the gel were evaluated. Finally, 71 type high temperature and high pressure water loss instrument and high temperature and high pressure filter with slit plate were used to evaluate the plugging capacity of gel plugging agent. The experimental results show that the new gel plugging system between 100°C - 120°C, gelation time can be controlled at about 5 h;it has strong temperature resistance, compression resistance, dilution resistance and gel breaking performance. In the face of permeability and fracture leakage simulation experiments, when the ambient temperature below 120°C, pressure within 5 MPa, the filter loss of gel plugging agent is far less than the market two conventional plugging agent, has excellent plugging performance.

Study on the Plugging System of the Lower Ancient High Loss Zone in Changqing Gas Field

At present, in the workover operations of old gas wells in the Changqing Gas Field, due to years of exploitation in the production layer, pressure deficits, and general leakage during the well killing, the well must be plugged before the well can be killed. In particular, the fracture-cavity type fractures of the lower paleocarbonate reservoirs have serious leakage. Traditional plugging materials and traditional plugging materials and methods have some limitations in dealing with leakage problems. Therefore, a composite plugging system using polymer solution as the base carrier fluid, multi-particle size rigid particles, expandable particles and modified fibers is developed. Its formula is: water + 2% polyacrylamide + 0.1% N, N-methylene bisacrylamide polymer gel is the base carrier fluid;the formulation of the particle plugging agent was continuously optimized through the CDL-II high temperature and high pressure dynamic and static plugging ability to plug the core. The final formulation of the plugging agent is: 1) 20% rigid particles (5 mm, 1 mm, 0.5 mm CCP-3 ratio 4:2:1) + 1% 3 mm expanded particles SMK-1 + 1% 1 ~ 2 mm fiber SRXW-10;2) 20% rigid particles (3 mm, 0.1 mm, 0.05 mm CCP-3 ratio 3:2:1) + 1% 3 mm expanded particles SMK-1 + 1% 1 ~ 2 mm fiber SRXW-10. The water swelling multiples of the granular plugging agent in salt water are all above 7 times, which meets the requirements of leak-proof plugging operations under high salinity;3% HCl is selected as the gel breaker, and the plugging system has a gel breaking rate of 95%;through the water plugging and profile control experimental system, the sand-filled pipe is used to simulate the plugging effect under high temperature and high pressure, and the plugging system can be sealed for 5 days at a high temperature of 110°C and a high pressure of 20 MPa to achieve a good plugging of the formation. It is expected that the developed plugging system has a good application prospect in future workover operations.

复杂泥页岩地层井壁稳定钻井液材料研究现状

针对复杂泥页岩地层钻井过程中频繁出现的井壁失稳问题,目前国内外已形成了用于稳定井壁的钻井液技术,包括泥页岩水化抑制技术、地层孔隙封堵技术和化学固壁技术。但以上多种技术均无法抑制泥页岩的表面水化作用,高温条件下快速封堵和化学固壁剂的效果也相当有限,因此井壁失稳问题仍难以解决。系统总结了复杂泥页岩地层井壁稳定钻井液材料的研究工作,通过对井壁稳定钻井液材料研究现状进行分析,阐述了不同钻井液材料包括泥页岩水化抑制剂、封堵剂、化学固壁剂的作用机理,探讨了不同种类井壁稳定材料的优势和缺陷。据此指出开展泥页岩水化基础理论研究、开发高温高盐条件下稳定有效的新型纳米材料、建立能够模拟井下条件的化学固壁剂的评价方法将成为未来复杂泥页岩地层井壁稳定钻井液材料和技术研究的热点和难点。最后对复杂泥页岩地层井壁稳定钻井液技术和材料的发展方向进行了展望。

乳化沥青提高原油采收率研究进展

乳化沥青具有注入性能好、封堵强度高等优点,作为一种选择性堵剂在油田提高采收率领域比其他化学剂体系更具应用潜力。本文总结了国内乳化沥青堵水体系的开发历程及现场选择性堵水的应用效果。通过调研近年来国内外文献,概述了乳化沥青堵水的作用机理,一种是作为乳液的作用机理,主要是乳液颗粒被变形捕获产生贾敏效应和乳液液滴的机械滞留使水的流动阻力增大;另一种是其分散相也就是乳液破乳后沥青的作用机理,主要是沥青黏附在岩壁上起到的堵水作用。同时,总结了乳化沥青稳定的主要影响因素,包括温度、水相中的电解质浓度和pH值以及分散相中的沥青质,并且论述了各因素影响乳化沥青稳定性的作用机理。最后,详细叙述了乳化沥青应用于油田调剖堵水领域的最新研究进展,研究表明乳化沥青不仅具有优异的封堵效果,还具有独特的封堵选择性。此外,乳化沥青还能与CO_(2)吞吐、泡沫调驱组成复合增产技术进行现场应用,并且指出了乳化沥青应用于调剖堵水领域存在的问题与未来展望。

延迟成胶弹性硅酸凝胶堵水剂及其性能研究

针对现有硅酸凝胶堵水剂普遍存在成胶时间短、成胶后脆性大的问题,结合L油田油藏条件,通过考察活化剂类型及用量,弹性改善剂类型及用量,以及水玻璃用量对成胶时间和弹性模量的影响,得出了一种延迟成胶弹性硅酸凝胶堵水剂。其配方为:6%水玻璃+0.85%活化剂三元弱酸一铵GL-1+0.1%弹性改善剂正电胶,该配方在油藏温度65℃下,成胶强度达到E级的时间为72 h,成胶后的弹性模量为589.46 Pa。采用填砂管实验评价了堵水剂的注入性及封堵性,结果表明堵水剂在L油田中具有良好的注入性及封堵性,在渗透率为1168.06×10^(-3)~5061.57×10^(-3)μm^(2)的填砂管中,注入0.8 PV的最高注入压力仅有0.72 MPa,封堵率均>96%。该堵水剂可用于L油田的油井堵水。

改性聚乙醇酸暂堵剂研发及其在河南油田的应用

酸溶性暂堵剂对地层伤害较大,解堵较麻烦,油溶性暂堵剂不适合高含水的油层;河南油田低渗透油藏地层温度为50~120℃,注水驱油见水快,常规水溶性聚乙醇酸暂堵剂和聚乳酸暂堵剂水解温度大于80℃,不能完全满足低渗透油藏暂堵压裂的需求。结合颗粒类水溶性聚乙醇酸暂堵剂和聚乳酸暂堵剂的特性和暂堵原理,采用催化剂和抑制剂使聚乙醇酸和聚乳酸发生酯化反应,生成聚乙醇酸和聚乳酸融合物,再加入成核剂及结晶促进剂,可得到改性聚乙醇酸暂堵剂。经测试,改性聚乙醇酸暂堵剂在50~120℃温度下具有常规聚乙醇酸暂堵剂的溶解性能和暂堵强度;当改性聚乙醇酸暂堵剂的总用量占比达到18%、粗粒径与细粒径质量配比接近1:1时,其封堵强度大于40 MPa,暂堵性能良好。现场试验7井次,加入改性聚乙醇酸暂堵剂后,单井施工压力最高增加了6.1 MPa,日增油5.3 t,取得了明显的增油效果。

矿用喷涂堵漏风自修复材料性能研究及工程应用

喷涂堵漏风是防止煤自燃的有效手段之一。针对传统水泥基喷涂堵漏风材料脆性大、易开裂、堵漏风效果差的弊端,提出以微生物及结晶矿物为自愈合剂,研制出生物胶囊和矿物胶囊以及一种生物–矿物–纤维协同自修复材料。研究了不同养护湿度和养护时间对材料裂缝自修复能力的影响。结果表明:当养护湿度为100%相对湿度、养护时间为35 d时,研制的生物胶囊和矿物胶囊可以将裂缝完全修复,裂缝最大修复宽度为1260μm。采用扫描电子显微镜(SEM)和X射线能谱仪(EDS)探究了自修复材料裂缝区域修复产物的晶型及元素组成,发现裂缝处的修复产物为球碳镁石、花瓣状的水菱镁矿以及大量由细菌矿化产生的球形方解石,这些修复产物在一定程度上起到了密闭裂缝的作用;EDS能谱分析证实了修复产物为MgCO_(3)和CaCO_(3)。当养护湿度为100%时,材料具有最高的堵漏风率(97.15%),比同养护条件的对照组试样高出73.62%。最后将自修复材料用于沿空煤柱喷涂堵漏风,结果显示该材料在6个月内未发现明显裂隙,与传统水泥砂浆相比,该材料具有更长的使用寿命和更好的预防效果。

低渗透油田微生物堵剂的多尺度封堵性能

封堵低渗透油藏的多尺度水窜通道是提升这类油藏水驱开发效果的关键,开发了一种内源微生物堵剂,优化了其菌种发酵营养液配方,并基于室内静态实验表征了其基础物性,最后通过岩心动态实验评价了其封堵适应性。所优化的菌种发酵营养液配方为:1.0%~2.0%糖蜜+0.2%~1.0%硝酸钠+0.5%~2.0%磷酸二氢钾+0.2%~1.0%磷酸氢二钠+0.1%~0.5%硫酸铵+0.01%~0.1%工业酵母膏+0.01%~0.03%硫酸铁+0.01%~0.03%硫酸锰。在营养液中培养4 d后,微生物趋于稳定,形成的分散颗粒呈正态分布,粒径集中在40~160μm之间,粒度中值在90μm左右,且具有良好的抗剪切性、耐盐性及稳定性。初始态的微生物调堵剂能顺利进入低渗透岩心、非均质岩心和裂缝性岩心。进入岩心后,微生物基于其自生长特性与孔隙及裂缝介质匹配,对渗透率为5×10^(-3)μm^(2)的岩心的封堵率达到80%;对渗透率为5×10^(-3)/100×10^(-3)μm^(2)的非均质岩心的封堵率达92%;对渗透率为5×10^(-3)/300×10^(-3)μm^(2)的非均质岩心的封堵率达95%。微生物堵剂对开度为30μm的裂缝性岩心的封堵率达84%;对开度为80μm的裂缝性岩心的封堵率接近90%。微生物堵剂既可以封堵不同尺度的多孔介质水窜通道,又可以封堵不同尺度的微裂缝水窜通道,具备封堵低渗透油田多尺度水窜通道的潜力。

海上某盆地胶结型防漏堵漏钻井液技术

分析了我国海上某盆地地质特征和历史井漏情况,明确了该盆地钻井防漏堵漏难点:地层裂缝发育且存在微米级至毫米级的多尺度裂缝,甚至裂缝和孔、洞并存,导致堵漏材料选配难、一次堵漏成功率低;地层发育大段风化壳、部分地层破碎严重、钻井中裂缝极易二次发育等,导致恶性漏失甚至失返性漏失等复杂情况。针对上述难点,以聚乙烯醇、聚丙烯酸以及含邻苯二酚结构的有机物为原料,合成了一种胶结型堵漏剂BFD-1。实验结果表明,人造疏松岩心在加有4%BFD-1的水溶液中浸泡后,岩心抗压强度提高率达19.34%。以BFD-1为核心,复配现场常用堵漏材料,构建了适用于不同尺寸范围漏失通道的防漏堵漏钻井液体系,具良好的防漏堵漏性、胶结性,并可有效阻止压力传递。研究成果可为该地区钻井井漏防治提供有力技术支撑。